1. Field of the Invention
This invention relates to a stator for a dynamoelectric machine in which a plurality of continuous strip-like yoke portions each having an integrally formed magnetic pole tooth are punched out of steel sheets, and a method of making such a stator.
2. Description of the Prior Art
One of conventional ring-shaped stator cores for dynamoelectric machines comprises a plurality of divided unit cores combined together into a single ring-shaped core. Each unit core comprises a number of unit steel sheets stacked on one another. Each unit steel sheet includes a plurality of core regions continuous via flexible portions with one another. A predetermined number of unit cores and unit magnetic pole teeth are integrally formed in each of the core regions. The unit steel sheets are stacked into each unit core and bent at the flexible portions into an arcuate shape. Each unit core thus formed has a developed configuration in which the core regions are linearly continuous via the flexible portions, and accordingly, each unit core is substantially linear rather than arcuate. Consequently, yield of the steel sheets is higher in the above-described unit steel sheet as compared with the case where each steel sheet is punched out into a ring-shaped, semicircular, quarter-circular or arcuate shape.
In the above-described construction, however, the unit steel sheets have a number of portions connected to one another in order that the plurality of divided unit cores may be connected to one another into a single ring-shaped core. Furthermore, each unit steel sheet has a number of portions at which the unit yokes are abutted against each other. These connected portions and abutted portions each inevitably have a higher magnetic resistance than portions at which the steel sheets are continuous to one another. Accordingly, the connected portions and abutted portions adversely affect magnetic properties of the stator yoke. Furthermore, it is not easy to connect the unit cores to one another so that each of the connected and abutted portions has a magnetic resistance as low as the other portions. Additionally, one of conventional stator making methods requires a step of inserting into each of the magnetic pole teeth a mechanically wound stator core. In this method, the stator core has a large opening slot structure for provision of spaces into which the coils are inserted. Large openings of the slots result in non-uniformity of the torque developed by the dynamoelectric machine.
Furthermore in the above-described method, the stator coil needs to be prevented from falling off or moving in the slots after the insertion. The structure for preventing falling-off or movement of the stator coil has been desired to be achieved in an easy manner.